The present invention relates to method and apparatus for managing steam systems, and more specifically, to the method and apparatus for automaticallly monitoring and eliminating condensate and air from steam systems and providing data regarding same.
Steam distribution systems have been used for many years for transferring heat from heat sources, such as conventional boilers and more recently, nuclear reactors, to points where the heat is utilized, such as for manufacturing processes, generating electrical or mechanical power, heating buildings, and other such uses. It is inherent in the nature of steam distribution systems that some of the steam condenses to water as heat of vaporization is lost from the steam by radiation and conduction to the substance or product being heated. Such condensate must be discharged or eliminated from the steam system immediately in order to maintain efficient heat distribution via the steam system because the heat content of condensate is negligible compared to that of steam. The condensate is also valuable, so it is usually returned to the boiler.
It is also inherent in such steam systems for air and non-condensable gases to become entrained in the steam, for example, by introduction into the steam system along with make-up water. Such entrained air and other non-condensables in steam systems also decrease efficiency of heat transfer by depressing obtainable temperatures at desired pressures and, more significantly, by creating a film on the interior heat transfer surfaces which is equivalent to an insulator and inhibits the transfer of heat from the steam to the apparatus or material which is to be heated. Small concentrations of air can dramatically reduce the film coefficient, i.e., inhibit the heat transfer. For example, a 1% concentration of air in a steam system can, in some instances, cause a 50% reduction in the film coefficient. Consequently, it is desireable, if not necessary, to purge steam distribution systems to eliminate air and other non-condensables therefrom.
Devices commonly known as steam traps are available for collecting and dumping condensate from steam systems. They are usually fitted on heat exchanger outlets and are intended to collect and discharge condensate while not permitting steam to escape. However, current steam trap technology prior to this invention does not permit rapid, efficient purging of air and other non-condensables from steam systems. A pervasive problem is that such current technology steam traps are also not very reliable devices for saving live steam either. In large installations with hundreds of steam traps, it is not unusual to find 10% of the traps to be malfunctioning. When a steam trap fails and allows live steam to blow through it and out of the system, it is the ultimate waste of energy in steam systems. It can also cause spoiled products, damage to plant facilities, and other unneeded costs. In most installations, it is estimated that the mean time to detect a "blowing trap" is two weeks.
Conventional steam traps utilize temperature or pressure sensitive elements, such as floats, discs, and the like, to shut off steam flow while intermittently or continuously draining condensate. They can, for the most part, be generally grouped into three categories: thermostatic traps, mechanical buoyancy traps, and thermodynamic traps.
Thermostatic traps use bimetallic elements to open and close condensate drains in response to the difference in temperature between hotter steam and cooler condensate. This type of trap is somewhat wasteful in that it passes live steam, and its operating components are not very durable.
Mechanical buoyancy traps operate on the basis of the density difference between steam and condensate. Floats, which are raised or lowered by the collecting condensate, open valves to remove condensate when the trap is full and close valves after the traps are emptied. These traps cannot pass non-condensable gas, such as air, under normal operating conditions. They can vapor lock, and they cannot be used in freezing environments. Also, this kind of mechanism tends to throttle the valve as it begins to close, allowing cutting and erosion in the valve that can ultimately result in valve failure that allows live steam to escape.
In a thermodynamic trap, pressure in the trap inlet pushes up a disc to allow discharge of condensate. Then, when hot steam and condensate reach the trap, the high velocity flow past the disc tends to reduce pressure under the disc allowing some condensate to flash. The flashing condensate over the disc forces it shut. This type of trap is also wasteful in that it allows passage of live steam therethrough during each condensate dump cycle. Also, high back pressure associated with these traps can affect their cycle rate.
Consequently, there remains a need in the industry for more efficient and effective steam management apparatus for collecting and disposing of condensate from steam distribution systems with durable and dependable valve mechanisms. There is also a need for a method and apparatus capable of automatically purging the air when some predetermined maximum acceptable level of air in the system is reached. It is also desireable to provide steam system management apparatus which allows the maintenance personnel to monitor the performance of the steam distribution system, the amount of condensate eliminated from the system, warning alarms for malfunctioning dump valves, and displays indicating condensate dumps, fills, air purges, and the like. Another feature that is needed is a reliable system for providing accurate data on the volume of condensate dumped from the steam system.
One of the impediments to developing more sophisticated steam system control and management apparatus is that the use of electronics for operating such apparatus could be hazardous. Often steam traps are positioned in tunnels or subbasements where potentially explosive gasses can accumulate and where the use of electrical equipment could create sparks that could set off an explosion. Also, electrical power is not always available where steam traps are located.